ZILLOW: Here are the US cities where the housing shortage is at 'crisis levels'

America's housing shortage is at "crisis levels," according to Zillow.

The number of homes available for sale fell for a third straight year in 2017, the firm said in a report on Thursday. There were 10% fewer homes on the market in December 2017 compared with December 2016.

"Aging millennials and young families may be able to find more affordable new homes for sale this year, but they'll most likely be in further-flung suburbs with more grueling commutes to urban job centers," said Aaron Terrazas, a senior economist at Zillow.

He added that tax cuts would put more money in buyers' pockets, increasing demand at a time when builders continue to struggle with rising land and labor costs.

The shortage is worse in some markets where home prices are rising faster.

Here are the 15 metro areas that experienced the biggest year-over-year declines in inventory as of December.